The present invention relates to a method for producing a stiffened hollow structure of a fiber-reinforced composite comprising a hollow skin portion and a stiffening portion, in which an adhesive provided between a skin member and a stiffener is uniformly and efficiently set with a tensile force.
Recently, it has been desired to reduce a weight of a transport machine such as an aircraft and an automobile from viewpoints of conservation of the global environment and energy-saving. Therefore, researches have been in progress for using a fiber-reinforced composite excellent in lightweight, strength, corrosion resistance, oil resistance, etc. for the transport machine.
Conventionally, members of the fiber-reinforced composite have been bonded to each other by adhesive. For instance, a method using an unhardened prepreg as the adhesive for bonding the members has been disclosed in Japanese Patent Laid-Open No. 10-264257. The fiber-reinforced composite members are generally glued together while applying a pressure thereto to uniformly spread the adhesive all over the adhesion surface. As a method for applying a pressure, (i) methods using a clamp or a pressing apparatus, (ii) methods using a screw, a bolt and nut, etc. to utilize a tightening force due to screwing torque for pressing, etc. have been known.
To bond large-sized fiber-reinforced composite members to each other, in general, the members have been settled on a large jig of a metal and fixed by a rivet, a bolt, a clamp, etc. In the case of using the bolt, etc., a large number of apertures for bolts should be formed in the fiber-reinforced composite members, and after the bonding, the bolts should be removed from the apertures and the apertures should be filled up. Thus, such conventional methods use the large jig and comprise a large number of steps to be remarkably costly.
Accordingly, an object of the present invention is to provide a method for producing a stiffened hollow structure, in which skin members and a stiffener each made of a fiber-reinforced composite are efficiently bonded together with reduced steps.
As a result of intensive research in view of the above object, the inventors have found that a stiffened hollow structure can be efficiently produced with reduced steps of disposing skin members on a stiffener through an adhesive, and setting the adhesive while applying a tensile force to the skin members and the stiffener by a band. The present invention has been accomplished by the finding.
Thus, a method of the present invention is for producing a stiffened hollow structure from a first skin member, a second skin member and a stiffener each made of a fiber-reinforced composite, the stiffened hollow structure comprising a hollow skin portion and a stiffening portion for strengthening the hollow skin portion from the inside, and the method comprises the steps of: (1) disposing the first skin member and the second skin member on the stiffener, an adhesive being provided between the stiffener and each of the first skin member and the second skin member; (2) placing a band on the outer surface of the first skin member and the second skin member; and (3) setting (or hardening) the adhesive while tightening the band and applying a tensile force to the first skin member and the second skin member.
In the method of the present invention, the adhesive is preferably a thermo-setting adhesion sheet, and the band is particularly preferably made of a carbon fiber-reinforced composite. Further, it is preferable that L-shaped angle plates are fixed on both ends of the band and that a tensile force-controlling shim is disposed between the L-shaped angle plates. It is preferred that one or two band is used for one adhesion portion, and it is also preferred that a buffer is disposed between the band and each of the first skin member and the second skin member.
The first skin member and the second skin member is preferably bonded such that an end portion of the first skin member and an end portion of the second skin member are overlapped each other through an adhesive, and a pressing force is applied to the end portions by a pressurizing jig comprising a magnet and a pressure-receiving jig of a magnetic material when the adhesive is set.
The method for producing a stiffened hollow structure according to the present invention is useful for the case where each of the first skin member and the second skin member has a semi-cylindrical shape and the stiffener has a cylindrical shape. Further, the method is particularly useful for producing a body structure of an aircraft composed of semi-cylindrical skin members and a body flame stiffening the skin members.